Am giving up on getting across the federal law concept or the constitutional basis for it. And apparently there is no way to really watch-list someone across all states for making lethal threats - easier for police and the shrinks they send in to dismiss it as just venting or whatever. So that would leave us with (a) let the shooting sprees continue and consider it acceptable collateral damage for FREEDUMB!!!!! or (b) have real comprehensive federal gun control. All that's needed is a SCOTUS decision that definitively clarifies what the 2nd amendment meant in 1790, and what can be applied to now. That opens up legislation that is responsive to the 21st century where we have armies with advanced weaponry that citizens cannot personally own.
Ukrainian soldiers aren't fending off Russian tyranny with rifles. Stingers, Javelins, drones, SAMs, etc. are what are helping them.
But how would that update of sensible legislation happen where gun manufacturers keep politicians in their pockets and bankroll enormous campaigns of media saturation? Where the makeup of SCOTUS is markedly to the right of most Americans?
Really, we'd need to ban lobbyists from all levels of government, and set term limits for SCOTUS justices and reform campaign finance.